What is this absurd equilibrium point? What is it measuring and how do you measure it?
You don't. That's the whole point. You just let it do its thing. Start with the city and free-flowing traffic. Whoopee - everyone will use their car. After a while, that results in congestion and delay. Some will put up with it, some will ditch their cars in favour of some other form of transport. Eventually, you each an equilibrium with a particular level of congestion that most people will tolerate. You can shift the equilibrium by (for example), opening a new bus route, tube line, cycle lane, etc, or you can shift it the other way by widening a road, building a flyover,etc. Or you can do it by regulation - congestion charging, low emissions zones, etc. After a while, following each intervention, a new equilibrium will establish itself.